Let me tell you a real incident, but I will exercise 'creative
judgement' and change details to protect the identities of people
involved. 
When I was still a Nursing Student doing an attachment in a local
hospital, my tutor and I was walking towards an MRT station when we
saw an elderly man who suddenly collapsed and lay on the floor,
looking quite dazed and weak.
I told my tutor, "Oh no! Let's go over and help that man!"
My tutor pulled me back saying, "No, let's just move on, see, there
are uniformed nurses who are going to help the man already! Let's
not invite trouble and get ourselves involved!" (It was the end of
a working shift so that's why there were nurses around the MRT
Station heading back home).
I was extremely stunned to hear her say that! Being my tutor, I
thought she should be a good example instead of holding me
back!
It was only much later that I sorta understood her reticence. She
was probably afraid of any unpleasant repurcussions. 
It's sad that the fear of any legal repurcussion would deter people
from helping, but the sad truth is, people ARE becoming more
litigatious these days, and unreasonably so too!
Imagine, doctor or not, nurse or otherwise, First Aid trained or
not, we all have our off days when we're tired or exhausted after a
day's work and am heading home in a 'switched off' mode. When
suddenly confronted with a collapsed man in such a situation, we
may rush forward to help but in our quick response, we may
inadvertently not do something right, or forget a few steps, etc.
Being CPR certified does not guarantee that you would not have any
off days or be caught off-guard or in your haste, miss a step or
two.
Of course, trained personnel have to be competent and there ought
to be no excuses about it. But things somehow don't always happen
as we wish, and the scenarios might not always have perfect
endings.
Bottom line is, whether an injury is incurred because of someone
trying to help or not, the person who stepped forward to provide
aid only had the best intention in mind and definitely did not have
the intention of harming the person. It was a benevolent act
stemming from a good heart. That should not be punished.
The counter effect that suing Good Samaritans would bring, is a
hesitant attitude in other Good Samaritans. Definitely, seeing a
fellow Good Samaritan be sued and get into trouble for trying to
help would deter fellow Good Samaritans from stepping up to help
someone without stopping to think twice, thrice, and more, before
doing so or worse, before finally thinking that it's better to
trash the thought, and just walk away.
If we allow Good Samaritans to suffer, we are simply breeding a
"help not" attitude in everyone else.